Though it hasn't received a full-fledged expansion like its sibling Dragon Age: Origins, Mass Effect 2 has been getting a steady stream of smaller-scale downloadable content since it went on sale in January. At a recent London press event, publisher Electronic Arts showed off the latest add-on for the sci-fi role-playing game, titled Overlord.

As outlined in GameSpot's brand-new preview, Overlord will be the fifth story-driven DLC for Mass Effect 2, following the Normandy Crash Site, Zaeed's "Price of Revenge" loyalty mission, five-mission Firewalker Pack (with new tank vehicle), and Kasumi's "Stolen Memory" loyalty mission. The first and last of those add-ons both added a new crew member and new weaponry to the game.

Due out in June, Overlord is being billed by developer BioWare as the "biggest downloadable content pack yet" for Mass Effect 2, which has sold over 1.6 million units in North America and Europe. Costing 560 Microsoft points or $7/£4.80, it will add five planets to the in-game galactic map, each of which can be explored with the hammerhead tank that was first featured in the Firewalker pack.

BioWare reps told GameSpot the add-on would feature exploration similar to--but would improve upon--the mako ATV missions in the original Mass Effect. The five planets will offer "expansive" maps and will be tied together by a plot about experiments with geth technology gone horribly wrong. At the center of the chaos is a malevolent artificial intelligence hunkered down in a heavily defended Cerberus research facility, which players must storm.

For more details on Mass Effect 2 Overlord, check out the GameSpot interview with producer Casey Hudson below.